Hi bulrush,
I’m assuming that you’ve read the mattress shopping tutorial here but two of the most important links in the tutorial that I would especially make sure you read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort” and PPP (Posture and alignment, Pressure relief, and Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists (based on all the parts of your personal value equation that are most important to you).
The better options or possibilities I’m aware of in and around the Grand Rapids area (subject to making sure that any mattress you are considering meets the quality/value guidelines I linked) are listed in post #273 here. There is also a list for the Kalamazoo/Portage area that is also reasonably close to you in post #2 here that may be helpful as well
Innersprings aren’t normally the weakest link in a mattress and the useful life of a mattress will depend much more on the types of materials or components that are on top of the innerspring than the innerspring itself.
There is also more about the pros and cons of different types of innersprings in this article and in post #10 here.
There is no way to quantify how long any mattress will last for a specific person or predict exactly when you will decide to replace it because it is no longer suitable or comfortable for you (because this is the only real measure of durability that counts) because there are too many unknowns and variables involved that are unique to each person but if a mattress is well inside a suitable comfort/support range and isn’t close to the edge of being too soft when it is new and meets the minimum quality/durability specs that are suggested in the guidelines here then it would be reasonable to expect a useful lifetime in the range of 7 - 10 years and with materials that are higher quality and more durable than the minimum guidelines (in the top comfort layers especially) it would likely be in the higher end of the range or even longer.
There is also much more detailed information about all the many variables that can affect the durability and useful life of a mattress relative to different people in post #4 here and the posts it links to.
Phoenix